Bibliographic details of the publications referred to by author in this specification are collected alphabetically at the end of the description.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.
Schizophrenia is one of the most disabling and emotionally devastating illnesses known to man. Unfortunately, because it has been misunderstood for so long, it has received relatively little attention and its victims have been undeservingly stigmatized. Schizophrenia is, in fact, a fairly common disorder. It affects both sexes equally and strikes about 1% of the population worldwide. Another 2-3% have schizotypal personality disorder, a milder form of the disease. Because of its prevalence and severity, schizophrenia has been studied extensively in an effort to develop better criteria for diagnosing the illness.
Schizophrenia is characterized by a constellation of distinctive and predictable symptoms. The symptoms that are most commonly associated with the disease are called positive symptoms, that denote the presence of grossly abnormal behaviour. These include thought disorder (speech which is difficult to follow or jumping from one subject to another with no logical connection), delusions (false beliefs of persecution, guilt, grandeur or being under outside control) and hallucinations (visual or auditory). Thought disorder is the diminished ability to think clearly and logically. Often it is manifested by disconnected and nonsensical language that renders the person with schizophrenia incapable of participating in conversation, contributing to his alienation from his family, friends and society. Delusions are common among individuals with schizophrenia. An affected person may believe that he is being conspired against (called “paranoid delusion”). “Broadcasting” describes a type of delusion in which the individual with this illness believes that his thoughts can be heard by others. Hallucinations can be heard, seen or even felt. Most often they take the form of voices heard only by the afflicted person. Such voices may describe the person's actions, warn him of danger or tell him what to do. At times the individual may hear several voices carrying on a conversation. Less obvious than the above “positive symptoms” and “thought disorder” but equally serious are the deficit or negative symptoms that represent the absence of normal behaviour. These include flat or blunted affect (i.e. lack of emotional expression), apathy, social withdrawal and lack of insight.
The onset of schizophrenia usually occurs during adolescence or early adulthood, although it has been known to develop in older people. Onset may be rapid with acute symptoms developing over several weeks, or it may be slow developing over months or even years. While schizophrenia can affect anyone at any point in life, it is somewhat more common in those persons who are genetically predisposed to the disease with the first psychotic episode generally occurring in late adolescence or early adulthood. The probability of developing schizophrenia as the offspring of two parents, neither of whom has the disease, is 1 percent. The probability of developing schizophrenia as the offspring of one parent with the disease is approximately 13 percent. The probability of developing schizophrenia as the offspring of both parents with the disease is approximately 35 percent. This is indicative of the existence of a genetic link.
Three-quarters of persons with schizophrenia develop the disease between 16 and 25 years of age. Onset is uncommon after age 30 and rare after age 40. In the 16-25 year old age group, schizophrenia affects more men than women. In the 25-30 year old group, the incident is higher in women than in men.
In general, the study of any illness requires that there should be good criteria for diagnosis. In fact, diagnosis should ultimately be based on causes i.e., on whether an illness results from a genetic defect, a viral or bacterial infection, toxins or stress. Unfortunately, the causes of most psychiatric illnesses are unknown and therefore these disorders are still grouped according to which of the four major mental faculties are affected:
(i) disorders of thinking and cognition
(ii) disorders of mood
(iii) disorders of social behaviour; and
(iv) disorders of learning, memory and intelligence.
Accordingly, since so little is known of the biological causes of these conditions, there is an ongoing need to elucidate the mechanisms by which these diseases are induced and progress.
The 14-3-3 proteins constitute a family of highly conserved regulatory molecules expressed abundantly throughout development and in adult tissue. These proteins comprise seven distinct isoforms (β, ζ, ϵ, γ, η, τ, σ), that bind a multitude of functionally diverse signalling molecules to control cell cycle regulation, proliferation, migration, differentiation and apoptosis (Berg et al. Nat Rev Neurosci 2003; 4(9):752-762; Fu et al. Annu Rev Pharmacol Toxicol 2000; 40:617-647; Toyo-oka et al. Nat Genet 2003 July; 34(3): 274-285; Aitken A. Semin Cancer Biol 2006; 16(3):162-172; Rosner et al. Amino Acids 2006; 30(1):105-109).
To date, the role, if any, of the protein 14-3-3 family of molecules in schizophrenia has remained elusive. Some research has focussed, albeit so far inconclusively, on identifying single nuclear polymorphisms associated with a predisposition to developing a neuropsychiatric condition such as schizophrenia. Studies aimed at investigating changes to levels of protein 14-3-3 isoforms, irrespective of whether or not those molecules are mutated, have tended to focus on changes to the levels of the eta and theta isoforms, although to date there has not been any conclusive-evidence that they are reliable markers of the onset of a neuropsychiatric condition. In relation to other of the protein 14-3-3 isoforms, such as beta and zeta, Wong et al. (2005) found no change to expression levels in schizophrenia and bipolar disorders. Middleton et al. (2005) went further and stated that these particular isoforms are not likely to be directly related to a genetic risk for developing schizophrenia and that neither marker provides a strong association with schizophrenia.
Nevertheless, and contrary to these findings, in work leading up to the present invention it has been determined that a reduction in the functional level of protein 14-3-3ζ is associated with the onset of or predisposition to the onset of a neuropsychiatric disorder, such as a condition which is characterised by one or more symptoms of schizophrenia. Still further, it has also been determined that a reduction in the level of protein 14-3-3ζ/DISC1 complex formation is similarly diagnostic. These findings have now facilitated the design of methodology to routinely and accurately screen individuals to confirm the onset of, or a predisposition to the development of, a neuropsychiatric disorder.